When recycling old paper, it is first pulped by machinery commonly called pulpers and this pulp then is rid of its diverse foreign bodies called contaminants by being sifted. However, following contaminant elimination, the pulp still contains ink particles which must be eliminated if the pulp is used to manufacture high-grade paper.
It is already known to eliminate ink particles by blowing air into the pulp using bubble-generating injectors: thereupon a foam composed of thousands of bubbles appears above the pulp, the ink particles clinging to the walls of said bubbles.
Much air-injection machinery with which to carry out such deinking already has been described, illustratively in the European patent application EP 0,305,251 filed by applicant and in the German patent DE 35 24 071.
The European patent EP 0,122,747 describes deinking machinery wherein air is injected into a duct through which flows a pulp and which issues into the bottom of a receptacle whereby the bubbles rise through the pulp to form a foam carpet at the pulp surface; the foam is then sucked away.
The German patent DE 35 24 071 describes deinking machinery consisting of an enclosure where the pulp to be deinked is introduced at the said enclosure upper level, said pulp circulating along a spiral from top to bottom through the enclosure, part of this pulp being removed from the enclosure to be aerated and reinjected at the base and at the center of the enclosure.
Research by applicant has discovered that pulp deinking efficiency using air bubbling will be significantly improved by increasing the likelihood the bubbles will collide with the ink particles as said bubbles pass through the pulp.
Now the above described machinery are inadequate in this respect because being designed in such manner that the collision probability of the bubbles and the ink particles and the bubble transit times through the pulp are inadequate.